1. Field of the Invention
The present invention relates to a vacuum insulator for being used as insulating material for a building or a refrigerator, etc.
2. Background Information
Half of total energy amount consumed by human being is for heating/cooling houses and commercial buildings, and this rate is same as domestic rate. Considering the fact that supply amount of alternative energy is only 1 to 2% of total energy consumption amount and supply amount for alternative energy is not above 10% even in a long term plan, reducing energy for heating/cooling is the most effective way to overcome this present energy crisis. The reason why much energy is consumed for heating/cooling is that heat conduction coefficient of conventional insulators still stays at threshold value of 30 mW/m·K for a last century. An idea for reducing energy consumption to half with the conventional insulating materials is to control the thickness of the insulating materials. However, in this idea, thickness of insulating materials is too thick to build economic buildings, and it inevitably requires breaking down conventional buildings.
Accordingly, a vacuum insulator has been developed as an ultra insulator capable of being used as interior and exterior materials of conventional and new buildings. The vacuum insulator is composed of a porous filler and an isolation envelope for surrounding the filler. Since the vacuum insulator removes gas in the envelope and keeps vacuum state in the envelope for a few years, the vacuum insulator can have a very low heat conduction rate. Since the vacuum insulator has a 10 to 100 times insulating efficiency compared to conventional insulating materials, the insulating effect can be increased by using the vacuum insulator. Since the thickness of the insulator compared to conventional insulating materials is decreased, utilization of internal space can be improved. In addition, since the inside of the vacuum insulator is kept vacuum, the convective heat conduction in the inside can be prevented. Here, the vacuum level in the vacuum insulator causes remarkable difference in vacuum efficiency, and thus it is important to keep the vacuum level in the vacuum insulator. Factors of increasing internal pressure and affecting the vacuum level in the vacuum insulator are gas escape from an internal structure, air infiltration from the envelope, and air infiltration through the envelope surface or the envelope adhesion part. The most influential one of those factors is the air infiltration through the envelope adhesion part.
In the conventional method, in order to prevent air infiltration through the envelope adhesion part, the adhesion part is adhered by heat with Low density polyethylene LDPE film and a Linear low density polyethylene LLDPE film having a high permeability.
FIG. 1 is a schematic diagram for showing a structure of a vacuum insulator according to the conventional technique.
As shown in FIG. 1, the vacuum insulator according to the conventional technique comprises an envelope 10, an internal structure 30 and a filler 40. The adhesion part 20 of four edges parts in which a Low density polyethylene film LDPE, an aluminium film, a Linear low density polyethylene LLDPE film are stacked, is adhered by heat. This envelope 10 prevents air infiltration from the outside.
FIG. 2a and FIG. 2b are cross sectional views of showing structures of the envelope of the vacuum insulator according to the conventional technique.
FIG. 2a is a cross sectional view of showing a structure of the envelope at an area cut along B-B of FIG. 1, and FIG. 2b is a cross sectional view of showing the structure of the envelope at an area cut along A-A of FIG. 1. Here, FIG. 2a is a cross sectional view of the envelope 10 of FIG. 1, and FIG. 2b is a cross sectional view of the adhesion part 20 of FIG. 1.
As shown in FIG. 2a, the envelope of a single film according to the conventional technique is composed of a Polyethylene terephthalate film PET 11, a Low density polyethylene film LDPE 12, an aluminium film 13, and a Low density polyethylene film LDPE 14 and a Linear low density polyethylene film LLDPE 15. Here, since the aluminium film at the middle of the envelope has a low permeability, air permeation from the outside through the envelope surface can be prevented.
As shown in FIG. 2b, in the adhesion part 20 where two envelops are adhered, the envelope of a single film composed of a Polyethylene terephthalate film PET 11a, a Low density polyethylene film LDPE 12a, an aluminium film 13a, and a Low density polyethylene film LDPE 14a and a Linear low density polyethylene film LLDPE 15a is adhered with another single layer envelope composed of a Linear low density polyethylene film LLDPE 15b, a Low density polyethylene film LDPE 14b, an aluminium film 13b, a Low density polyethylene film LDPE 12b and a Polyethylene terephthalate film PET 11b. 
Here, the two envelopes are adhered by heat the Low density polyethylene film LDPE 14a, 14b and the Linear low density polyethylene film LLDPE 15a, 15b. However, the Low density polyethylene film LDPE 14a, 14b and the Linear low density polyethylene film LLDPE 15a, 15b have a problem of making air infiltration easy through the adhesion part because of its high air permeability.
In addition, since vacuum level in the vacuum insulator is not kept due to the reasons, insulating efficiency can be reduced remarkably. In addition, since insulating efficiency of the vacuum insulator is reduced remarkably, the vacuum insulator can not perform its role.